Question

But, not wanting to necro it and using this as an opportunity to gather all recent information into one thread, I'm starting this here.

To state nothing new: In the vanilla state, freshly installed, the 64bit KSP (for quite some time now) is not able to connect to the TrackIR 5 software. The user could work around this problem by replacing the TrackIRUnity.dll in the KSP_Data/Managed folder with this one: https://github.com/medsouz/Unity-TrackIR-Plugin-DLL/releases.

However, this does no longer work in KSP 1.2.1x64.

TrackIR 5.4 does no longer connect to the 64bit Unity application at all, with or without fixed DLL.

Still a problem in KSP 1.2 -- workaround still works.
I know it's low priority, but it's also a 2 second fix: just replace the file -- it's not exactly rocket science (ironic). ;-)

However this is no longer the case for KSP 1.2.1x64. The vanilla DLL that comes with the clean install AND the supposed fix do no longer provide a connection between the TrackIR 5 software and the game engine.

I'm also aware there is a community modification for Headtracking equipment of all kinds, found here:

However, the DLL provided by this mod has the same problem on a 64bit install as the supposed 'fix' (likely the same). I myself was using KerbTrack up until KSP 1.2, then the update to 1.2.1 broke headtracking completly for me (and others I imagine). I ruled out the update replacing the fixed DLL with the stock one by replacing it again, still no joy.

As I want this thread to become an easy to use hub for users with the same problem, I'll edit this post with the solution once there is one I know of.